As red phosphors, nitride phosphors such as CaAlSiN3:Eu and (Sr,Ca)AlSiN3:Eu, and sulfide phosphors such as (Ca,Sr)S:Eu are well known, but composite fluoride phosphors represented by the general formula A2MF6:Mn4+ (where the element A is Li, Na, K, Rb, Cs, NH4 or the like, and the element M is Ge, Si, Sn, Ti, Zr or the like) have attracted interest as red phosphors having an extremely sharp fluorescence spectrum and having high brightness while having a deep red color. These phosphors have a structure in which Mn4+ is substituted as a solid solution at some of the tetravalent element M sites, and exhibit a fluorescence spectrum that combines multiple narrow-band emissions due to electron transitions in the Mn4+.
As a method for producing such composite fluoride phosphors represented by A2MF6:Mn4+, Patent Document 1 discloses a production method that involves preparing a reaction solution into which some of the constituent elements of the fluoride phosphor are dissolved, and adding the remaining constituent elements in the form of compounds in the solid state or in a reaction solution. In particular, the document describes a method wherein the raw material compounds are added and mixed, at a predetermined ratio, with hydrofluoric acid, and after all of the raw material compounds have dissolved, an organic compound-based poor solvent such as methanol, ethanol or acetone is added and the solubility is reduced to cause precipitation of the phosphor. Similarly, Patent Document 2 also describes that acetone was added to cause precipitation of a phosphor.
However, with the production method described in Patent Document 1 or 2, there is a tendency for the optical properties of the precipitated phosphor to be insufficient. The reason for this is believed to be due to the fact that, with methods that involve adding an organic compound-based poor solvent when causing precipitation of a phosphor, the Mn4+, which is the emission center, is not stably and sufficiently incorporated into the phosphor. Additionally, when an organic compound-based poor solvent is added, substances other than the constituent elements of the phosphor become intermixed therein, thus resulting in impurities and loss of luminescence efficiency.